#define __GUN_SOURCE__
#include <errno.h>
#include <netdb.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <unistd.h>

#define PORT 5555
#define MAXMSG 512

int make_socket(uint16_t port)
{
    int sock;
    struct sockaddr_in name;

    /* Create the socket. */
    sock = socket(PF_INET, SOCK_STREAM, 0);
    if (sock < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    /* Give the socket a name. */
    name.sin_family = AF_INET;
    name.sin_port = htons(port);
    name.sin_addr.s_addr = htonl(INADDR_ANY);
    if (bind(sock, (struct sockaddr *)&name, sizeof(name)) < 0) {
        perror("bind");
        exit(EXIT_FAILURE);
    }

    return sock;
}

int read_from_client(int filedes)
{
    char buffer[MAXMSG];
    int nbytes;

    nbytes = read(filedes, buffer, MAXMSG);
    if (nbytes < 0) {
        /* Read error. */
        perror("read");
        exit(EXIT_FAILURE);
    } else if (nbytes == 0)
        /* End-of-file. */
        return -1;
    else {
        /* Data read. */
        fprintf(stderr, "Server: got message: `%s'\n", buffer);
        return 0;
    }
}

int main(void)
{
    extern int make_socket(uint16_t port);
    int sock;
    fd_set active_fd_set, read_fd_set;
    int i;
    struct sockaddr_in clientname;
    size_t size;

    /* Create the socket and set it up to accept connections. */
    sock = make_socket(PORT);
    if (listen(sock, 1) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    /* Initialize the set of active sockets. */
    FD_ZERO(&active_fd_set);
    FD_SET(sock, &active_fd_set);

    while (1) {
        /* Block until input arrives on one or more active sockets. */
        read_fd_set = active_fd_set; // 
        if (select(FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0) {
            perror("select");
            exit(EXIT_FAILURE);
        }
        //active_fd_set 0,1,2,3,4,5,6,7,8,9
        //read_fd_set 0, 8, 9
        /* Service all the sockets with input pending. */
        for (i = 0; i < FD_SETSIZE; ++i) // fd 属于 [0 - FD_SETSIZE)
            if (FD_ISSET(i, &read_fd_set)) {  // select 会拷贝回来可以读的 fd
                if (i == sock) {
                    /* Connection request on original socket. */
                    int new;
                    size = sizeof(clientname);
                    new = accept(sock, (struct sockaddr *)&clientname, &size);
                    if (new < 0) {
                        perror("accept");
                        exit(EXIT_FAILURE);
                    }
                    fprintf(stderr, "Server: connect from host %s, port %hd.\n",
                            inet_ntoa(clientname.sin_addr), ntohs(clientname.sin_port));


                    FD_SET(new, &active_fd_set);
        // 0,1,2,3,4,5,6,7,8,9,10

                } else { // accept fd
                    /* Data arriving on an already-connected socket. */
                    if (read_from_client(i) < 0) {
                        close(i);
                        FD_CLR(i, &active_fd_set);
                    }
                }
            }
    }
}
